Study on the Selectivity of Benzoylation of Metal Chelates of Sucrose1

Abstract

A study of the selectivity of metal chelate-directed benzoylation of sucrose dianion, relative to unchelated sucrose anion, was conducted as part of a study on new synthetic approaches to the high-potency sweetener sucralose. Ionic complexes of sucrose with various metal ions were prepared in DMF and the resulting complexes reacted at low temperature with benzoic anhydride. Cobalt and manganese salts directed esterification mostly to the 3′-OH on the fructosyl portion. Unchelated sucrose anion and other metals favored esterification at the 2-OH of the glucosyl portion. Migration of the benzoate ester along the glucose portion was observed in the direction O-2 to O-6 at moderate temperature, but at higher temperature transannular migration was observed from the glucose to the fructose ring. Reaction mixtures were analyzed by HPLC and monobenzoates identified by retention times relative to standards. Six of eight possible monobenzoates of sucrose were isolated from mixtures and identified by their ¹H NMR spectra.     

Degradation of Sucrose,Glucose and Fructose in Concentrated Aqueous Solutions Under Constant pH Conditions at Elevated Temperature

ABSTRACT

The degradation of sucrose can decrease sucrose yield, reduce the efficiency of sugar factory and refinery processes, and effect end product quality. Characterization of sucrose degradation under modeled industrial processing conditions will underpin further technological improvements. Effects of constant reaction pH on sucrose degradation were investigated using simulated industrial model systems (100 °C; 65 °Brix [% dissolved solids]; N₂; 0.05-3 mol NaOH titrant; 8 h), with the use of an autotitrator. Reaction pH values ranged from 4.40 to 10.45. Polarimetry and ion chromatography with integrated pulsed amperometric detection (IC-IPAD) were used to quantify sucrose degradation and first-order reaction constants were calculated. Minimum sucrose degradation occurred between pH 6.45 - 8.50, with minimum color formation between pH's 4.40 - 7.00. Polarimetry, often used in U.S. sugar factories and refineries to monitor chemical sucrose losses, was shown not to be viable to measure sucrose degradation under alkaline conditions, because of the formation of fructose degradation products with an overall positive optical rotation. For comparison, fructose and glucose (80 °C; 65 °Brix; N₂; 3 mol NaOH; 2 h) were also degraded at constant pH 8.3 conditions. For sucrose, fructose, and glucose, formation of organic acids on degradation was concomitant with color formation, indicating they are probably produced from similar reaction pathways. For the glucose and fructose degradation reactions, color and organic acid formation also were highly correlated (R²>0.966) with changes in optical rotation values, confirming that these compounds are formed from similar reaction pathways.     

Comparison of adsorption equilibrium of fructose, glucose and sucrose on potassium gel-type and macroporous sodium ion-exchange resins

Adsorption equilibrium of fructose, glucose and sucrose was evaluated on sulfonated poly(styrene-co-divinylbenzene) cation-exchange resins. Two types of resins were used: potassium (K⁺) gel-type and sodium (Na⁺) macroporous resins. Influence of the cation and effect of the resin structure on adsorption were studied. The adsorption isotherms were determined by the static method in batch mode for mono-component and multi-component sugar mixtures, at 25 and 40 °C, in a range of concentrations between 5 and 250 g L⁻¹. All adsorption isotherms were fitted by a linear model in this range of concentrations. Sugars were adsorbed in both resins by the following order: fructose > glucose > sucrose. Sucrose was more adsorbed in the Na⁺ macroporous resin, glucose was identically adsorbed, and fructose was more adsorbed in the K⁺ gel-type resin. Data obtained from the adsorption of multi-component mixtures as compared to the mono-component ones showed a competitive effect on the adsorption at 25 °C, and a synergetic effect at 40 °C. The temperature increase conducted to a decrease on the adsorption capacity for mono-component sugar mixtures, and to an increase for the multi-component mixtures. Based on the selectivity results, K⁺ gel-type resin seems to be the best choice for the separation of fructose, glucose and sucrose, at 25 °C.     

Fluorometric Determination of Fructose, Glucose, and Sucrose Using Zirconyl Chloride

Zirconyl chloride upon hydrolysis in water to form Zr(OH)⁺ has been found to react to form a fluorescent derivative with not only a ketose such as fructose but also a hexose such as glucose and the disaccharide sucrose. When reaction conditions such as a temperature of 99°C and a time of 60 min are used, detection limits below 1 μg/mL are possible. All three zirconyl–sugar derivatives show very similar absorbance and fluorescence spectra, indicating a common mechanism involving formation of an enediol which can be complexed with ZrOH⁺ is likely. Because the reactivity order is glucose < sucrose < fructose, the reaction can be made selective for fructose at a lower reaction temperature and time such as 60°C at 5 min. Because interference from ascorbic acid and caffeine is also avoided, the fluorescent determination of fructose in soft drink samples after simply a dilution step is possible. We have also employed this reaction for flow injection analysis (FIA) using a polystyrene–divinylbenzene-packed HPLC column as a mixing device. Using a 0.01 M HClO₄ with 1% zirconyl chloride carrier, we obtained a linear calibration curve from 2 to 30 μg/mL with a correlation coefficient of 0.994. A detection limit less than 2 μg/mL was possible. A comparison of results for the FIA of soft drinks with the enzymatic method involving fructose-5-dehydrogenase confirmed the FIA method was quite specific for fructose.     

红枣中果糖、葡萄糖与蔗糖的高效液相色谱示差检测分析

建立了同时分析鲜红枣中果糖、葡萄糖和蔗糖的高效液相色谱方法.利用鲜红枣样品进行添加回收实验,获得方法对果糖、葡萄糖和蔗糖测定的平均回收率分别为93.5%、91.8%和89.8%,变异系数3.27%、2.34%、5.86%.结果表明:采用高效液相色谱示差分析方法定量检测鲜红枣中果糖、葡萄糖和蔗糖快速、简便.同时得出方法的检出限为:果糖5.73×10-3mg/mL,葡萄糖5.22×10-3mg/mL,蔗糖3.59×10-3mg/mL,测定结果符合食品检测要求.     

Curing and Glass Transition of Epoxy Resins from Ester-Carboxylic Acid Derivatives of Mono- and Disaccharides,and Alcoholysis Lignin

Mono- and disaccharides (SAC) such as glucose (Glc), fructose (Frc) and sucrose (Suc), and also alcoholysis lignin (AL) were dissolved in ethylene glycol and each of the obtained mixtures was reacted with succinic anhydride to form a mixture of ester-carboxylic acid derivatives such as SAC-polyacid, SACPA, and AL-polyacid, ALPA. Ethylene glycol-polyacid (EGPA) was also prepared from ethylene glycol. Each of the obtained mixtures of ester carboxylic acid derivatives was reacted with ethylene glycol diglycidyl ether in the presence of a catalytic amount of dimethylbenzylamine to form ester-epoxy resins. The molar ratios of epoxy groups to carboxylic acid groups ([EPOXY]/[ACID] ratios, mol mol⁻¹) was maintained at 1.0. The contents of SACPA and ALPA in the mixtures of SACPA/EGPA, and ALPA/EGPA, respectively, were also varied from 0 to 100 %. The curing reaction of SucPA and ALPA was studied by differential scanning calorimetry (DSC). Activation energy of the curing reaction for the SucPA system was 80.5 kJ/mol. Thermal properties of epoxy resins were studied by DSC. Glass transition temperatures (T_g) decreased with increasing numbers of repeating units in ester chains between cross-linking points, suggesting that ester chain lengths between cross-linking points mainly affect the mobility of ester chains in epoxy resin networks.     

Extraction,purification procedures and HPLC-RI analysis of carbohydrates in olive (Olea europaea L.) plants

Summary Qualitative and quantitative analyses of carbohydrates in olive (Olea europaea L.) tissues have been carried out by HPLC-RI. Sample purification was by two successive solid-liquid extractions to remove completely plant phenolics and pigments. Five carbohydrate peaks; sucrose (stachyose + raffinose + sucrose), glucose, galactose, fructose (fructose + myo-inositol) and mannitol were detected when plant extracts were run on a Sugar SC 1011 column operating at 75°C, using water as eluent 0.5 ml min⁻¹. The use of two serial Sugar SC 1011 columns operating at 90°C and eluting the plant extracts with H₂O−CH₃CN (95/5 v/v) enables identification and quantification of nine carbohydrates, including tetra and tri-saccharides.     

Determination of reducing sugars with a 2,4-dinitrophenolate-selective membrane electrode

A 2,4-dinitrophenolate-selective liquid-membrane electrode based on tetrapentylammonium dinitrophenolate dissolved in 2-nitrotoluene is described. The electrode exhibits rapid and near- Nernstian response to the activity of 2,4-dinitrophenolate anions in the range 3×10^?5 ?1×10^?2 M. The response is unaffected by pH in the range 7.5–12.5. The electrode has been successfully applied to the kinetic potentiometric determination of fructose, glucose and galactose at 60°C and of fructose in the presence of glucose and galactose at 30°C. The electrode can be used for the potentiometric determination of glucose and fructose after completion of the reaction with excess of 2,4-dinitrophenolate ions and of sucrose after acid hydrolysis. Mixtures of glucose, fructose and sucrose in aqueous solutions or honey samples can be determined by the proposed procedures with an average error of about 2%.     

Continuous chromatographic separation of glucose-fructose mixtures using anion-exchange resins

Summary A semi-continuous, counter-current chromatographic refiner (SCCR) was packed with an anion resin in the bisulphite form and used to separate mixtures of sugars from different feedstocks. Products with purities of more than 99% were achieved and solid concentrations of the fructose products of 12% w/v were possible. The deterioration of the anion resin was controlled by simple precautions and thus its useful life was substantially prolonged.     

Effect of Different Ionic Liquids on 5-Hydroxymethylfurfural Preparation from Glucose in DMA over AlCl3: Experimental and Theoretical Study

In this work, effect of different ionic liquids (ILs) on 5‐hydroxymethylfurfural (HMF) preparation from glucose in N,N‐dimethylacetamide (DMA) over AlCl₃ was revealed by a combined experimental and computational study. ILs used as cocatalysts in this work included N‐methyl‐2‐pyrrolidone hydrogen sulfate ([NMP]HSO₄), N‐methyl‐2‐pyrrolidone methyl sulfate ([NMP]CH₃SO₃), N‐methyl‐2‐pyrrolidone chlorine ([NMP]Cl) and N‐methyl‐2‐pyrrolidone bromide ([NMP]Br) which were endowed with the same cation but different anions. According to the conclusion that fructose was intermediate product from glucose to HMF, we found fructose was transformed to more by‐products by [NMP]HSO₄, making HMF yield decline significantly when glucose was treated as substrate. Neither glucose nor fructose could be converted by [NMP]CH₃SO₃ efficiently, leading to its no influence on glucose conversion to HMF. [NMP]Br had a higher selectivity for HMF from fructose than [NMP]Cl and AlCl₃. Besides, Al³⁺ preferred to combine with Br^?, slightly decreasing both the overall free energy barrier for glucose isomerization and activation barrier for H‐shift at 393.15 K. So a high HMF yield of 57% was obtained from glucose catalyzed by AlCl₃ together with [NMP]Br under mild conditions.     

Cathodized Gold Nanoparticle‐Modified Graphite Pencil Electrode for Non‐Enzymatic Sensitive Voltammetric Detection of Glucose

A highly sensitive enzymeless electrochemical glucose sensor has been developed based on the simply prepared cathodized gold nanoparticle‐modified graphite pencil electrode (AuNP‐GPE). Cyclic voltammetry (CV) experiments show that AuNP‐GPE is able to oxidize glucose partially at low potential (around −0.27) whereas the bare GPE cannot oxidize glucose in the entire tested potential windows. Besides, fructose and sucrose cannot be oxidized at potential lower than +0.1 V at AuNP‐GPE. As a result, the glucose oxidation peak at around −0.27 V is suitable enough for selective detection of glucose in the presence of fructose and sucrose. Cathodization of AuNP‐GPE under optimum condition (‐1.0 V for 30 s) in the same glucose solution before voltammetric measurement enhanced glucose oxidation peak current around −0.27 V to achieve an efficient electrochemical sensor for glucose with a detection limit of 12 μM and dynamic range between 0.05 to 5.0 mM with a good linearity (R²= 0.999). Almost no interference effect was observed for sensing of glucose in the presence of ascorbic acid, alanine, phenylalanine, fructose, sucrose, and NaCl.     

A kinetic spectrophotometric method for the determination of ternary mixtures of reducing sugars with the aid of artificial neural networks and multivariate calibration

A differential spectrophotometric method has been developed for the simultaneous quantitative determination of glucose (GLU), fructose (FRU) and lactose (LAC) in food samples. It relies on the different kinetic rates of the analytes in their oxidative reaction with potassium ferricyanide (K₃Fe(CN)₆) as the oxidant. The reaction data were recorded at the analytical wavelength (420 nm) of the K₃Fe(CN)₆ spectrum. Since the kinetic runs of glucose, fructose and lactose overlap seriously, the condition number was calculated for the data matrix to assist with the optimisation of the experimental conditions. Values of 80 °C and 1.5 mol l⁻¹ were selected for the temperature and concentration of sodium hydroxide (NaOH), respectively. Linear calibration graphs were obtained in the concentration range of 2.96-66.7, 3.21-67.1 and 4.66-101 mg l⁻¹ for glucose, fructose and lactose, respectively. Synthetic mixtures of the three reducing sugar were analysed, and the data obtained were processed by chemometrics methods, such as partial least square (PLS), principal component regression (PCR), classical least square (CLS), back propagation-artificial neural network (BP-ANN) and radial basis function-artificial neural network (RBF-ANN), using the normal and the first-derivative kinetic data. The results show that calibrations based on first-derivative data have advantages for the prediction of the analytes and the RBF-ANN gives the lowest prediction errors of the five chemometrics methods. Following the validation of the proposed method, it was applied for the determination of the three reducing sugars in several commercial food samples; and the standard addition method yielded satisfactory recoveries in all instances.     

Determination of sugars in depilatory formulations: a green analytical method employing infrared detection and partial least squares regression

A green analytical method was developed for the analysis of sugar-based depilatories. Three independent partial least squares (PLS) regression models were built for the direct determination of glucose, fructose and maltose without any sample pretreatment based on their attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectra. The models showed adequate prediction capabilities with root-mean-square-errors of prediction ranging from 7.04 to 12.55 mg sugar g⁻¹ sample. As a reference procedure, gradient liquid chromatography with on-line infrared detection, employing background correction based on cubic smoothing splines, was used. The analysis revealed changes in the sugar concentration due to the formulation process as compared to information on the ingredients provided by the manufacturers. Although fructose, glucose and sucrose were declared to be used for the production of depilatories, in the final products only fructose, glucose and maltose were determined. This fact was attributed to pH and temperature conditions employed during the production process as well as to the use of glucose syrup instead of crystalline glucose. The present ATR-FTIR-PLS method enables an accurate, cheap and fast determination without solvent consumption or toxic waste generation and offers therefore a green screening alternative to methods employing chromatographic techniques.     

The measurement of activity coefficients for solutes at infinite dilution with mixed solvents formamide + glucose,or + fructose,or + sucrose using a gas liquid chromatography at 298.15 K

Using gas liquid chromatography, activity coefficients for nine solutes at infinite dilution (γ_i^∞) in stationary solvent of formamide + glucose, + fructose and + sucrose at 298.15 K have been measured. Linear dependence of ln γ_i^∞ on the mole fraction of sugar was observed.     

Preparation and characterization of Ni(II)/polyacrylonitrile and carbon nanotube composite modified electrode and application for carbohydrates electrocatalytic oxidation

A nickel(II) into porous polyacrylonitrile–carbon nanotubes composite modified glassy carbon electrode (Ni/PAN-CNT/GCE) was fabricated by simple drop-casting and immersing technique. The unique electrochemical activity of Ni/PAN-CNT composite modified glassy carbon electrode was illustrated in 0.10?M NaOH using cyclic voltammetry. The Ni/PAN-CNT/GCE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni/PAN/GCE and Ni/CNT/GCE. The results of electrochemical impedance spectroscopy and scanning electron microscopy indicated the successful immobilization for PAN-CNT composite film. Kinetic parameters such as the electron transfer coefficient, α, and rate constant, k _s, of the electrode reaction were determined. Ni/PAN-CNT/GCE also shows good electrocatalytic activity toward the oxidation of carbohydrates (glucose, sucrose, fructose, and sorbitol). The electrocatalytic response showed a wide linear range (10–1,500, 12–3,200, 7–3,500, and 16–4,200?μM for glucose, sucrose, fructose, and sorbitol, respectively) as well as its experimental limit of detection can be achieved 6, 7, 5, and 11?μM for glucose, sucrose, fructose, and sorbitol, respectively. The modified electrode for carbohydrates determination is of the property of simple preparation, good stability, and high sensitivity.     

Molecular aspects of glucose dehydration by chromium chlorides in ionic liquids

A combined experimental and computational study of the ionic‐liquid‐mediated dehydration of glucose and fructose by Cr^II and Cr^III chlorides has been performed. The ability of chromium to selectively dehydrate glucose to 5‐hydroxymethylfurfural (HMF) in the ionic liquid 1‐ethyl‐3‐methyl imidazolium chloride does not depend on the oxidation state of chromium. Nevertheless, Cr^III exhibits higher activity and selectivity to HMF than Cr^II. Anhydrous CrCl₂ and CrCl₃?6 H₂O readily catalyze glucose dehydration with HMF yields of 60 and 72 %, respectively, after 3 h. Anhydrous CrCl₃ has a lower activity, because it only slowly dissolves in the reaction mixture. The transformation of glucose to HMF involves the formation of fructose as an intermediate. The exceptional catalytic performance of the chromium catalysts is explained by their unique ability to catalyze glucose to fructose isomerization and fructose to HMF dehydration with high selectivity. Side reactions leading to humins by means of condensation reactions take predominantly place during fructose dehydration. The higher HMF selectivity for Cr^III is tentatively explained by the higher activity in fructose dehydration compared to Cr^II. This limits the concentration of intermediates that are involved in bimolecular condensation reactions. Model DFT calculations indicate a substantially lower activation barrier for glucose isomerization by Cr^III compared to Cr^II. Qualitatively, glucose isomerization follows a similar mechanism for Cr^II and Cr^III. The mechanism involves ring opening of D ‐glucopyranose coordinated to a single Cr ion, followed by a transient self‐organization of catalytic chromium complexes that promotes the rate‐determining hydrogen‐shift step.     

Enzyme Thermistor Analysis of Kinetics and Stability of Immobilized Invertase

Abstract

The kinetic behaviour of immobilized invertase was investigated using calorimetric measurements in an enzyme thermistor device. The hydrolysis of sucrose is an exothermic process with inhibition-like kinetics above 300 mmol/1; glucose gave no measurable heat of reaction and fructose molecules are condensed in an endothermic process. The concentration dependence of the temperature signal of fructose condensation is linear up to 2 mol/1 at an optimal pH of 3.3, and the absolute value of the heat of reaction is only 25% compared with that of the hydrolytic reaction. A higher K_m-value and a lower V_max are therefore assumed. The reaction heat of hydrolysis of sucrose decreases with increasing product concentration. A shift of the equilibrium by increasing concentrations of both products is accompanied by a competitive condensation reaction in the case of fructose. The stability of invertase in aqueous ethanol solutions was also investigated. It depends on the ethanol concentration and on the time of contact with the solvent. At 30% ethanol no inactivation within 20 min. occurs, whereas at 60% ethanol a linear dependence of the inactivation on the time of contact was found. Above 80% ethanol less than 10% enzymatic activity remained after a five-minute treatment. This irreversible inactivation has to be considered if invertase is applied in water miscible organic solvents.     

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5‐Hydroxymethylfurfural over Mesoporous Nb and Nb‐W Oxides

A series of mesoporous Nb and Nb‐W oxides were employed as highly active solid acid catalysts for the conversion of glucose to 5‐hydroxymethylfurfural (HMF ). The results of solid state ³¹P MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Brønsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb‐W oxides varied with the ratio of Brønsted to Lewis acid sites and high glucose conversion was observed over Nb₅W₅ and Nb₇W₃ oxides with high ratios of Brønsted to Lewis acid sites. All Nb‐W oxides show a relatively high selectivity of HMF , whereas no HMF forms over sulfuric acid due to its pure Brønsted acidity. The results indicate fast isomerization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Brønsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2‐butanol/H₂O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over Nb₇W₃ oxide. The 2‐butanol/H₂O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb₅W₅ oxide.     

Preparation of some 14C-labeled sugars by radiophotosynthesis using sugar beet whole plant

Uniformly labeled [¹⁴C]glucose, [¹⁴C]fructose, and [¹⁴C]sucrose with specific activities of several microcuries per millimole have been photosynthetically prepared using the whole sugar beet plant. Smaller amounts of high specific activity sugars have been found in the leaves while larger amounts with relatively lower specific activities have been found in the root. The specific activity of the products could be significantly increased by increasing the specific activity of the initially used radioactive carbon dioxide.     

Enzymeless determination of total sugar by luminol–tetrachloroaurate chemiluminescence on chip to analyze food samples

Chemiluminescence (CL) emission from luminol–tetrachloroaurate ([AuCl₄]^?) system studied in presence of monosaccharide sugars such as glucose and fructose was investigated on a microfluidic chip fabricated by the soft lithography technique. CL emission from the luminol–[AuCl₄]^? system at 430?nm was intensified remarkably by the catalytic activity of glucose and fructose at room temperature. Under optimized conditions, the CL emission intensity of the system was found to be linearly related to the concentration of the sugars. Based on this observation, nonenzymatic determination of total sugar (glucose, fructose, or hydrolyzable sucrose) was performed in a rapid and sensitive analytical method. The results revealed that the linearity ranged from 9 to 1,750?μM for glucose and 80 to 1,750?μM for fructose, with a limit of detection of 0.65 and 0.69?μM, respectively. The relative standard deviations determined at 250?μM based on six repetitive injections were 1.13 and 1.15?% for glucose and fructose, respectively. The developed method was successfully applied for determination of the total sugar concentration in food and beverages.